This invention relates to a piezoelectric motor comprising a piezoelectric component connected to a resonator and a movable element interacting with the resonator. Furthermore, the invention relates to a method for avoiding failure of such a piezoelectric motor. Contrary to known piezoelectric motors, it is not attempted to avoid wear in the contact portion between the resonator and the movable element, but instead it is attempted to specifically use that wear for optimizing the motor properties and for increasing the motor performance.
Several piezoelectric motors comprising a piezoelectric component connected to a resonator and a movable element interacting with the resonator are known in the prior art. In these motors, piezoelectric components, which vibrate mechanically when an appropriate electric voltage is applied thereto, are interactively connected to a resonator, which in turn contacts a movable element. The resonator transforms the vibrations of the piezoelectric component into preferably elliptical oscillations of the contacting portion between the resonator and the movable element. The movable element preferably moves in a first direction when a first voltage with a first frequency is applied to the piezoelectric component, and further moves in a second preferably opposite direction when a second voltage with a second frequency is applied to the piezoelectric component.
By way of these piezoelectric motors, electrically operated actuators can be moved over very exactly adjustable distances. This motion is silent to human hearing and consumes especially little energy. The piezoelectric motors are particularly cheap to manufacture. These piezoelectric motors can be used where a compact design requires a motor with little space requirements or where no or only small magnetic fields may be generated during operation.
Piezoelectric motors are mass products that, for example, in children's toys cause certain elements to move, or that in vehicles electrically deploy or actuate a variety of elements such as the ash tray or the side view mirrors. However, in all applications, one needs to ensure that the motors do not suffer a major loss of performance during operation and thus fail after a brief period of operation or do not perform their task in a satisfactory fashion anymore.
One goal of the invention is, therefore, to provide a piezoelectric motor that does not have the disadvantages of the prior art, and to provide a method for reducing the risk of failure of a piezoelectric motor during its life time.
This invention also relates to further piezoelectric motors that comprise at least one piezoelectric component connected to a resonator, and a movable element that interacts with the resonator. Furthermore, this invention relates to a method for manufacturing such a piezoelectric motor and also relates to a method for the excitation thereof.
Piezoelectric motors of the type just mentioned are known from the prior art that the Applicant has created. Therein, piezoelectric components, which vibrate mechanically when an appropriate electric voltage is applied thereto, are coupled to a resonator, which itself abuts a movable element. The resonator transforms the vibrations of the piezoelectric component into preferably elliptical vibrations of the resonator contact portion that touches the movable element. The movable element preferably moves in a first direction when a first voltage having a first frequency is applied, and moves in a second, preferably opposite direction when a second voltage having a second frequency is applied.
Having particularly low energy consumption and particularly low manufacturing cost, these piezoelectric motors allow moving electrically operated actuators over very exactly tunable distances in a manner that humans cannot hear. These piezoelectric motors have applications where a compact design requires a motor with little space requirements, or also where no or only few magnetic fields may be generated during operation.
Piezoelectric motors are mass produced products that, e.g., in toys for children, cause individual elements to move, or that in cars electrically extend, or adjust the position of, the ash tray or the side view mirror.
Examples of the piezoelectric component and the resonator are described in DE 100 62 672 A1 and in the unpublished German patent application with file number 101 41 820.5 (which was published as DE10141820 A1). There, the resonator is coupled to the piezoelectric component and transfers its vibrations onto the movable element. In doing so, the resonator preferably vibrates close to one of its natural modes. An example of an embodiment of the piezoelectric motor has been described in WO 01/41228A1 (the disclosure of which is now U.S. Pat. No. 6,768,245) or in the application having the file number PCT/EP01/03245 (the disclosure of which is now U.S. Pat. No. 6,690,101). All the patent applications mentioned above are incorporated herein by reference and are thus considered a part of this disclosure.
In typical piezoelectric motors, the excitation signal is transmitted to the piezoelectric component with a frequency that causes the resonator to vibrate in a natural mode. These resonance frequencies generate high vibration amplitudes and thus are generally considered to be advantageous modes of operation that have advantageous piezoelectric motor performance characteristics. The performance characteristics in this case are the forces that arise in the region of the contact portion between the resonator and the movable element, as well as velocities.
When piezoelectric motors are mass produced, it is important to achieve high reproducibility of the vibration modes that are transmitted from the piezoelectric component to the resonator. In particular, those vibration modes are crucial that occur in the region of the contact portion between the resonator and the movable element, whose motion is caused by the transferred vibrations.
The type of vibration mode at the contact portion fundamentally depends on the resonator geometry and the clamping location of the piezoelectric component within the resonator. Experience has shown that the reproducibility of the desired modes of operation and the reproducibility of the desired piezoelectric motor performance characteristics in many cases require a finishing step during the production of piezoelectric motors.
It is also a purpose of the invention to provide a piezoelectric motor that does not have the disadvantages of the prior art and to provide a method that considerably simplifies the manufacture of piezoelectric motors and their excitation.